1. Field of the Invention
The present invention relates to manufacturing. In particular, the present invention relates to a method of making a product having a surface configuration for improved buffing and the product itself. More particularly, the present invention relates to a method of making a golf ball product having a surface configuration for improved buffing and the golf ball product itself.
2. Description of the Related Art
Conventionally, golf balls are made by molding a cover around a core. The core may be wound or solid. A wound core typically comprises elastic thread wound about a solid or liquid center. Solid cores typically comprise a single-piece, solid center or a solid center covered by one or more mantle or boundary layers of material. Wound cores may also include one or more mantle layers.
The cover may be injection molded, compression molded, or cast molded over the core. Injection molding typically requires a mold having at least one pair of mold cavities that mate to form a spherical recess. In addition, a mold may include more than one mold cavity pair. A core is held within the center of the mold and liquid cover material is introduced into the mold around the core. With reaction injection molding (RAM), two or more reactive components are used to form the layer material. The components are mixed just prior to or simultaneously with injection into the mold.
Compression molds also typically include multiple pairs of mold cavities, each pair comprising first and second mold cavities that mate to form a spherical recess. In one exemplary compression molding process, a cover material is preformed into half-shells, which are assembled around each core. The assemblies are placed in the mold cavities, and the mold is closed. The core and cover combination is then exposed to heat and pressure, which cause the cover half-shells to combine and form a full cover.
Casting processes also typically utilize pairs of mold cavities. In a casting process, a cover material is introduced into a first mold cavity of each pair. A core is then either placed directly into the cover material or is held in position (e.g., by an overhanging vacuum or suction apparatus) to contact the cover material in what will be the spherical center of the mold cavity pair. Once the cover material is at least partially cured (e.g., to a point where the core will not substantially move), the cover material is introduced into a second mold cavity of each pair, and the mold is closed. The closed mold is then subjected to heat and pressure to cure the cover material thereby forming a cover on the core.
These processes may also be used to form an intermediate layer over the core.
As a common feature of injection molding, compression molding, and cast molding, when used to form a golf ball cover, the mold cavities typically include a pattern of protrusions to impart a dimple pattern on the cover during the molding process. Conventional dimples are depressions that act to reduce aerodynamic drag and increase aerodynamic lift. These dimples are formed where a dimple wall slopes away from the outer surface of the ball, forming a depression.
Although the preferred dimple is circular when viewed from above, the dimples may be oval, triangular, square, pentagonal, hexagonal, heptagonal, octagonal, etc. Possible cross-sectional shapes include, but are not limited to, circular arc, truncated cone, flattened trapezoid, and profiles defined by a parabolic curve, ellipse, semi-spherical curve, saucer-shaped curve, sine curve, or the shape generated by revolving a catenary curve about its symmetrical axis. Other possible dimple designs include dimples within dimples and constant depth dimples. In addition, more than one shape or type of dimple may be used on a single ball, if desired. See U.S. Pat. No. 5,556,943 and U.S. patent application Ser. Nos. 10/077,090 and 09/989,191, which are incorporated herein by reference in their entireties.
The dimples on a golf ball are important in reducing drag and increasing lift. Drag is the air resistance that acts on the golf ball in the direction opposite the ball's flight direction. As the ball travels through the air, the air that surrounds the ball has different velocities and, thus, different pressures. The air exerts maximum pressure at a stagnation point on the front of the ball. The air then flows around the surface of the ball with an increased velocity and reduced pressure. At some separation point, the air separates from the surface of the ball and generates a large turbulent flow area behind the ball. This flow area, which is called the wake, has low pressure. The difference between the high pressure in front of the ball and the low pressure behind the ball acts to slow the ball down. This is the primary source of drag for golf balls. The dimples on the golf ball cause a thin boundary layer of air adjacent the outer surface of the ball to flow in a turbulent manner. The turbulence energizes the boundary layer and helps move the separation point further backward, so that the layer stays attached further along the outer surface of the ball. As a result, there is a reduction in the area of the wake, an increase in the pressure behind the ball, and a substantial reduction in drag.
Once the dimpled cover is formed, the covered core is removed from the mold (demolded). Once demolded, golf balls usually require finishing process steps, such as buffing, surface preparation, painting, logo application, etc. Since molding requires the use of two or more mold parts, extra material frequently collects at the union of the mold parts during the molding process. This “flash” is removed by buffing the area of the cover that was adjacent the mold parting line. Known buffing processes generally involve the use of sanding belts, grinding wheels, or rotary cutting tools to remove the flash material. Typically, it also removes some dimpled cover material in the immediate vicinity of the seam. This makes the adjacent dimples shallower than intended. This also distorts the dimple shape, giving them a pointed, football-like outline. Additionally, this enlarges the dimple spacing across the parting line, since part of the dimple adjacent the seam line is removed. This adversely effects the aerodynamics of the golf ball by creating shallower dimples and an enlarged no-dimple band around the ball equator. This also creates an unbalanced look to the ball. If the distortion is severe enough, it can cause the ball to fail the USGA symmetry test, which states that a golf ball must not be designed or manufactured to have properties which differ from those of a spherically symmetrical ball.
Known attempts to compensate for these effects include deepening and/or enlarging the dimples adjacent the seam line and/or positioning the dimples closer to the seam line. However, buffing of these balls still results in distorted dimples along the parting line.
What is needed is a golf ball design, mold, and manufacturing method yielding a better post-buff golf ball.